A system with multiple transmit and receive antennas has recently attracted interest to increase the reliability or throughput of signal transmission and reception in wireless communication systems. Such a system is called a MIMO system and there are a plurality of modes supporting the MIMO system (i.e., MIMO modes). Depending on whether a transmitter receives channel information feedback from a receiver, the MIMO modes are categorized into open-loop (OL) mode and closed-loop (CL) mode. Channel information is not fed back in the OL mode whereas channel information is fed back in the CL mode. A MIMO system using the OL mode is called an OL-MIMO system and a MIMO system using the CL mode is called a CL-MIMO system. The OL-MIMO system adopts space time coding (STC) in order to increase diversity order or multiplexing order, and the CL-MIMO system uses a different transmission scheme depending on whether there is a single or multiple receivers. If channel information feedback is very accurate, dirty paper coding (DPC) mode is used, in which the transmitter transmits data with channel interference eliminated.
At present, a unified MIMO system supporting both the OL mode and the CL mode is proposed. For efficient utilization of resources, a receiver notifies a transmitter (i.e., a base station (BS)) of its channel status, and the BS allocates resources to the receiver according to the channel status in the unified MIMO system.
However, as the number of receivers increases, feedback information also increases. As a result, resource efficiency decreases in the unified MIMO system.
Accordingly, there exists a need for a technique for reducing the amount of feedback information in the unified MIMO system.
There is also a need for a technique for selecting an optimal MIMO mode from among a plurality of MIMO modes, taking into account the environment of a receiver in the unified MIMO system.